The research to be performed during the project period is designed to extend our understanding of the psychobiology of stress and coping in human newborns, infants and toddlers. Three groups of studies are proposed to examine young children's behavioral and physiological responses to stress. The focus of the research is on the pituitary-adreno-cortical system, a neuroendocrine system that plays a central role in stress resistance. The goals of the research include characterizing the adrenocortical response to normally occurring stressors in the lives of young children. These stressors include heelsticks, inoculations, and handling in early infancy, and psychosocial stressors such as interaction with strangers, separation, and approach-avoidance conflicts in older infants and toddlers. A second goal is to examine basal adrenocortical activity and its relations to the stress response. A third goal is to examine the relations between adrenocortical activity and infant behavioral responses to stress and to understand these relations Within the context of individual differences in temperament, parentinfant interaction, and parental personality and temperament. A final, major goal is to begin to develop paradigms for examining the links between adrenocortical activity and other stress- and emotion-sensitive physiological systems. Finally, pilot studies are proposed to extend the research to "at risk" populations of infants and young children. The research offers considerable promise in increasing our understanding of stress and coping processes in the developing child.